Rhizobitoxine as a post-emergent herbicide

ABSTRACT

RHIZOBITOXINE, A PHYTOTOXIC COMPOUND SYNTHESIZED BY THE BACTERIUM RHIZOBIUM JAPONICUM, IS COMBINED WITH A SPECIFICALLY FORMULATED SOLUTION OF SURFACTANT AND WETTING AGENT TO PROVIDE POST-EMERGENT HERBICIDAL ACTIVITY.

' o 3,672,862 United States Patent Ofice son et al. (Nature 183, 308-9, 1959) showed that this i 3 672 862 RHIZOBITO APOS'LEMERGENT phytotoxin exhibited a broad-spectrum toxicity to many HERBICIDE weed and crop seedlings when applied to sterile root Lowell D. Owens, Greenbelt, Md., assignoito the United solutions but they were unsuccessful in their attempts to States of America as represented by the Secretary of 5 demonstrate post-emergent herbicidal activity by leaf ap- NAigi'icultureC fin ti rt f r fi S N plication.

0 l'awlllgon :1 Q 131 lca Most of the post-emergent herbicides now in use pos- ZSZJINI7S 1958- Thls aPPhcahon 1969 sess one or more undesirable characteristics such as low 9 Int. CL A01 9/00 biodegradability in soil or toxicity to animals. In contrast, rhizobitoxine is readily degraded and rendered nontoxic in U.S. Cl. 7179 2 Claims two or three days by soil microorganisms. Furthermore,

a study of its mechanism of toxicity indicates that it would ABSTRACT OF THE DISCLOSURE not be toxic to animals. It is known to be a highly potent inhibitor of an enzyme found in microorganisms and Rhizobitoxine, a phytotoxic compound synthesized by 15 plants but not in animals the Pacterium RhiZO-bium japonicum' is combmed a Scientists have long felt that the undesirable character- SPeclfimllY .rmulated suflactam i Wemng istics, especially low biodegradability in soil exhibited b agent to Pmvlde post'emergem herblcldal actlvlty' most post-emergent herbicides posed a serious problem and that a herbicide that could be applied to the leaf and exhibit post-emergent activity without these undesir- A P e urqocable royahy'free hcense m the able characteristics was sorely needed. Even Johnson cited invention herein described, throughout the world for all above failed to Show posbemergent herbicidal activity p p of t Umted States Govemfneglti-glth pover when he applied the phytotoxin to the leaves. In view of 0 grant Subhcense; g Snell 12 E f is: Y grante to the history of the art and especially the negative results of the Ci q f O f Umte talfas Johnson, the present inventor had no reason to expect Th.ls apphqanqn o a commuanon'm'part 0 our that rhizobitoxine would be efiective as a post-emergent pending application for patent, Ser. No. 757,117 filed herbicide when applied to the leaves P 1968 now abandoned Itis an object of this invention to provide a means by This invention relates to rhizobitoxine and more spewhi h b cifically to its use as a post-emergent herbicide. C r 120 93 can e utl lzed efiectwely as a P emergent herbicide.

Rhizobitoxine is a phytotoxic compound synthesized by the bacterium Rhizobium japonicum and is isolated and Another i of f 15 to PTOVlde a P ifi d f cultures f Rhizobium japonicum (Plant emergent herbicide that is quickly biodegradable and non- Physiol. 40, 931-933, 1965). Although the exact structoxic to 3111111315- ture of the compound is unknown, a partial characteriza- In general, according to this invention the foregoing tion has been published (Bact. Proc., p. 19, 1967). Johnobjects are accomplished by employing a specifically for- EFFECT OF LEAF-APPLIED RHIZOBIUM PHYTOTOXIN ON WEEDS AND CROPS Leafstage when Toxin treatment X treated Micro- Micro- Treatment efiects 3 No. of grams liters of leaves of toxin solution P.p.m. 4th day 14th day Pigweed 4 10 20 500 Somenecrosis Some necrosis, growth abo t n l,

100 20 5,000 Plants dying Plants dead. Control 20 0 No efiect No effect.

Crabgrass 3 10 20 500 Severe chlorosis Severe chlorosis, growth somewhat t 100 20 5, 000 Moderate chlorosls. Severe chlorosis, growth stopped. Control 20 0 No effect No efiect.

Com (var. U .S. 13) 6 10 20 500 Light chlor0sis.. Appearance and growth about normal,

100 20 5, 000 Moderate chloros1s. Some chlorosis, growth somewhat stunted. Control 20 0 No effect N0 efiect.

Cotton (var. Coker 100)... 2 10 20 500 None None.

100 20 5,000 Severe chlorosis Light chlorosls, growth somewhat stunted. Control 20 0 No effect N o eflect.

Soybean (var. Lee) 2 10 20 500 Moderate chlorosis 1re ppearance and growth normal.

50 1, 250 Severe chlorosis odei'ate chlorosis and necrosis, growth severely stunted 200 40 5, 000 -.do Plants dead. Control 40 0 No efiect No effect.

Sorghum 2 2 5 400 Moderate chlorosis. Light ehlorosis, growth stunted.

10 10 l, 000 Severe chlorosis Severe chlorosis, growth stopped. 10 5,000 -do Severe chlorosis, plants dying. Control 10 0 No efiect.

Ra e var. Dwarf Essex 2 10 20 500 None.

p 20 5, 000 Plants dead Control 20 0 o efie Ryegrass (annual) 2 10 2 500 Moderate chlorosis Some necrosis and stunting or growth,

30 0.6 5,000 --do Do. Control 2 0 No efiect No efiect.

Wheat, 2 10 20 500 Light leaf-tip chlorosis Appearance and growth about normal.

100 20 6,000 -.do Do. Control 20 0 No efiect No effect.

1 Listed are the actual weights (micrograms) of toxin applied in the indicated volumes (microliters) of surfactant-wetting agent solution containing the specified concentrations (p.p.m.) oi toxin in parts toxin per million of solution (weight per volume basis). Control treatments were the indicated volumes of surfactant-wetting agent solution withouttoxin.

3 The chlorosis damage listed was observed only in the new leaf-growth which occurred soon after phytotoxin application. Leaves emerging a we k r more after application were often normal in appearance. Also, leaves fully developed before toxin application remained green.

mulated solution of surfactant and wetting agent in which to dissolve rhizobitoxine to obtain post-emergent herbicidal activity. Of several mixtures tested, toxicity is obtained only with a solution consisting essentially of ethanol:water: glycerol (50:50:1 on a volume basis) in which the phytotoxin is dissolved in concentrations ranging up to 5000 parts of toxin per million of solution (weight per volume basis). As can be seen in the table, the solution in which the phytotoxin is dissolved has no phytotoxic or other effect when applied in the same quantity and manner. as the phytotoxin solution.

A number of experiments showed that the phytoxin was toxic at low concentrations to many weed and crop species. Pure rhizobitoxine was dissolved in the previously noted surfactant-wetting agent solution and applied with a micropipette to the leaves of 4- to 21-day old seedlings of nine plant species. Toxic effects ranging from chlorosis to growth stunting and death were obtained with from 10 to 200 micrograms of rhizobitoxine per plant. These amounts are equivalent to about 0.01 to 0.2 pound per acre assuming a treated leaf area of 10 cm. per plant. In comparison, the potent broad-spectrum herbicide, amino-triazole, is commonly applied at the rate of about 0.5 pound per acre. 7

As shown in the table, rhizobitoxine stopped the growth of or killed five of the species tested and was generally toxic to the other four species. 1

I claim:

. 1. In a process of killing pigweed by'applying a phytotoxin to the leaves of the pigweed, the step of applying to the primary leaves of a 4 to 21 day old pigweed seedling 100 micrograms of rhizobitoxine, said rhizobitoxine being dissolved in microliters of a solvent mixture consisting of 50 parts ethanol, 50 parts water and 1 part glycerol, said rhizobitoxine killing the pigweed within 14 days of application and said rhizobitoxine being degraded and rendered nontoxic by soil microorganisms within 3 days of application.

2. In a process for killing rape by applying a phytotoxine to the leaves of the rape, the step of applying to the primary leaves of a 4 to 21 day old rape seedling 100 micrograms of rhizobitoxine, said rhizobitoxine being dissolved in 20 microliters of a solvent mixture consisting of 50 parts ethanol, 50 parts water and 1 part glycerol said rhizobitoxine killingthe rape within 14 days'of application and said rhizobitoxine being degradedand rendered nontoxic by soil microorganisms within 3 days ofapplication. 7

References Cited UNITED STATES PATENTS OTHER- REFERENCES Johnson et al., Responses of seedlings to extracts of soybean nodules (1959) Nature 183, pp;'308-09 (1959). Owens et al., Rhizobial-induced chlorosis in soybeans ctc., (1965), Plant Physiol. 40, PP- 927-30 (1965). i

Owens et al., Production of the soybean-chlorosis toxin etc., (1965), Plant Physiol, 40, pp. 931-33 (1965). Chailakhyan et al., Growth subs. in the secretion of Rhizobium spp. (1965), CA63, p. 16828 (1965).

Owens et al., Rhiz'obium induced phytotoxin etc.

Klingman, Weed Control As A Science (1966), Wiley & Sons Inc., November 1966, New York, pp. 52 and 53 1966).

. LEWIS GOITS, Primary Examiner v 71--76, Dig. 1 

